Liquid Crystal Structures Research Articles

Propagation of optical spatial solitons in nematic liquid crystals with quadruple power law of nonlinearity appears in fluid mechanics

Abstract The present research explores nematicons in liquid crystals (LCs) with quadruple power law nonlinearity utilizing the modified extended Fan sub-equation technique as an analytical tool to investigate the optical spatial soliton solutions. For the inaugural time, a novel version of nonlinearity is investigated in relation to LCs. There are distinct applications for the several wave solutions that have been created in optical handling data. The aforementioned modified extended Fan subequation approach offers novel, comprehensive solutions that are relatively easy to deploy in comparison to earlier, regular methodologies. This approach translates a coupled non-linear partial differential equation into a coupled ordinary differential equation through implementing a traveling wave conversion. This approach indicates that a large variety of traveling and solitary solutions that rely upon five parameters can be incorporated by the nematicons in LCs. In addition, the investigation yields solutions of the single and mixed non-degenerate Jacobi elliptic function form. Novel solutions, such as the periodic pattern, kink and anti-kink patterns, N-pattern, W-pattern, anti-Z-pattern, M-pattern, V-pattern, complexion pattern and anti-bell pattern, or dark soliton solutions of nematic LCs, have been constructed by means of modified extended Fan subequation technique through granting suitable values for the parameters. The computer software Mathematica 14 is used to illustrate several modulus, real and imaginary solutions visually in the form of contour, 2D, and 3D visualizations that help understand the concrete importance of the nematicons in LCs. This research additionally offers a physical comprehension of the obtained solutions and applications of model. The imposed approach is ultimately thought to be more potent and effective than alternative approaches, and the solutions found in this work could be beneficial in our understanding of soliton structures in LCs.

Pressure-induced phase transition from monomers to dimers in liquid crystals

ABSTRACT The crystal structures of liquid crystals, particularly various oligomers, have garnered significant attention, laying the groundwork for developing new materials and devices. Here, we demonstrate pressure plays a crucial role in the structure of liquid crystals. High-pressure Raman and photoluminescence spectra were on 5CB (4-cyano-4’−pentylbiphenyl) liquid crystal. Upon compression, the appearance of prominent fluorescence peaks suggests a phase transition. The Raman peaks, reflecting the C–H and C≡N bonds, exhibit splitting at a pressure of 3.2 GPa, further confirming the pressure-induced phase transition. The splitting is consistent with earlier calculations on the stretching vibration of the C≡N bond for various oligomers and indicates a phase transition from monomers to dimers in 5CB liquid crystal. The opposite shifts in Raman modes under pressure, specifically the blue-shift of C–H bonds and the red-shift of C≡N bonds, indicate that pressure enhances intermolecular interactions and leads to conjugation between the electrons on the C≡N bonds and the C–H bonds, resulting in dimer formation. Our findings not only reveal a novel strategy for producing oligomers in liquid crystals through the application of high pressure but also highlight that Raman spectroscopy is a valid, non-contact method for investigating the mechanisms of oligomerization.

Modelling nematic liquid crystal in fractal dimensions

In this paper we present a fractal Berreman's model which account for azimuthal surface anchoring of nematic liquid crystals which play a leading role nowadays in biomedical field and pharmaceutical controlled release dosage forms. The model is based on the concept of "product-like fractal measure" in anisotropic media which permits to describe liquid crystals formation in terms of fractal dimensions. It was observed that fractal dimensions affect both the polar azimuthal angle and the Franck excess elastic energy density of the distortion. For fractal dimensions close to unity, our analysis reveals the emergence of fluctuations and large deformations in the dynamical variables of the theory which suggest the presence of non-linear elastic instabilities or emergence of defect structures in liquid crystals. These fluctuations fade away for fractal dimensions much less than unity. We have evaluated the elastic energy per unit of area which is found to depend on the square of the fractal dimension. This leads to a decrease of the saturation voltage which is necessary to reduce the elastic energy of liquid crystals films in order to minimize the elastic energy. This reduction may describe nematic liquid crystals free from deformations, singularities or weak anchoring surfaces.

How smectic-A and smectic-C liquid crystals resolve confinement-induced frustration in spherical shells.

The layered structure of smectic liquid crystals cannot develop unobstructed when confined to spherical shells with layers extending in the radial direction, since the available cross section area increases from the inside to the outside of the shell yet the number and thickness of layers must be constant. For smectic-A (SmA) liquid crystals, with the layer normal m parallel to the director n, the frustration breaks up the texture into spherical lune domains with twist deformations of alternating sense, overlaid with a herringbone-like secondary modulation and mediated via localized bend regions where the boundary conditions are violated. The SmC phase has more degrees of freedom to resolve the frustration thanks to its non-zero tilt angle τ between n and m, but its response to tangential shell confinement was never studied. We show experimentally and theoretically that the lunes in shells undergoing a SmA-SmC transition become twice as wide and half as many and they lose the secondary modulation, adopting a configuration with no layer twist but uniform layer bend if τ reaches a large enough value. Our study expands our understanding of how smectics respond to spherical confinement and it opens new soft matter research opportunities, given the rich diversity of phases with SmC-like symmetry, including chiral and spontaneously polarized phases.

Hexagonal liquid crystals as emerging quasi solid-state electrolytes for aqueous lithium-ion batteries

The increasing market demand ranging from portable electronics to electric vehicles drives the advancement of lithium-ion batteries. However, traditional liquid electrolytes used in LIBs are plagued by issues such as leakage, vaporization, and the degradation of active materials, which compromise performance and pose safety risks. To address these challenges, herein, the liquid-crystalline electrolytes with hexagonal phase were designed based on the self-assembly of amphiphilic molecules, which exhibit both high ionic conductivity and a high Li+ transference number. The hexagonal liquid crystal structure reconfigures the Li+ solvation structure and provides a transport pathway for the Li+ structural diffusion, facilitating the efficient transport of Li+ and contributing to the high ionic conductivity. Furthermore, the ordered arrangement of amphiphilic anion significantly restricts anion diffusion, resulting in an exceptionally high Li+ transference number of 0.92. Additionally, when utilizing NaV3O8 (NVO) as the anode and LiMn2O4 (LMO) as the cathode, the resultant full cell delivers impressive rate performance and stable cycling performance. This work highlights the potential of lyotropic liquid crystals in the development of high-performance quasi solid-state electrolytes for aqueous lithium-ion batteries and beyond.

Single-step synthesis of shaped polymeric particles using initiated chemical vapor deposition in liquid crystals.

We elucidate a previously unknown synthesis pathway that leads to polymeric nanospheres, orientation-controlled microgels, or microspheroids via single-step polymerization of divinylbenzene (DVB) using initiated chemical vapor deposition (iCVD) in liquid crystals (LC). iCVD supplies vapor-phase reactants continuously, avoiding the critical limitation of reactant-induced disruption of LC structure that has plagued past LC-templated polymerization processes. LC is leveraged as a real-time display of the polymerization conditions and particle emergence, captured using an in situ long-focal range microscope. Detailed image analysis unravels key LC-guided mechanisms during polymerization. pDVB forms nanospheres due to poor solubilization by nematic LC. The nanospheres partition to the LC-solid interface and further assemble into microgel clusters whose orientation is guided by the LC molecular alignment. On further polymerization, microgel clusters transition to microspheroids that resemble liquid drops. We identify key energetic factors that guide trajectories along the synthesis pathway, providing the fundamental basis of a framework for engineering particle synthesis with shape control.

Liquid Crystal Ordering in Densely Packed Colloidal Suspensions of Highly Anisotropic Monolayer Nanosheets

Monolayer nanosheets of zirconium phosphate in aqueous suspension exhibit short-range repulsion and long-range attraction, producing, at overall volume fractions larger than about half a percent, phase separation into higher-concentration liquid crystal and lower-concentration isotropic regions. At high concentrations, this phase separation takes the form of an emulsion of condensed, liquid-crystalline droplets, which anneal to form lens-shaped tactoids. These tactoids provide an opportunity to study the liquid crystal ordering of inorganic nanosheets in the limit of large shape anisotropy (diameter/thickness~400) and high packing fraction (volume fraction ≳ 70%). The internal liquid crystal structure of the tactoids remains nematic even under conditions that would usually favor ordering into lamellar smectics. Local lamellar ordering is suggested by short-range, smectic-like layer correlations, but a full transition into a smectic phase appears to be inhibited by the nanosheet edges, which act as a perturbative population of dislocation loops in the system of layers. Under conditions of thermal equilibrium, the nanoplates organize positionally to enable bend deformation of the director, a hallmark of the nematic phase and its principal distinction from the smectic, where bend must be expelled.

Imaging with a twist: Three-dimensional insights of the chiral nematic phase of cellulose nanocrystals via SHG microscopy.

Cellulose nanocrystals (CNCs) are bio-based nanoparticles that, under the right conditions, self-align into chiral nematic liquid crystals with a helical pitch. In this work, we exploit the inherent confocal effect of second-harmonic generation (SHG) microscopy to acquire highly resolved three-dimensional (3D) images of the chiral nematic phase of CNCs in a label-free manner. An in-depth analysis revealed a direct link between the observed variations in SHG intensity and the pitch. The highly contrasted 3D images provided unprecedented detail into liquid crystal's native structure. Local alignment, morphology, as well as the presence of defects are readily revealed, and a provisional framework relating the SHG response to the orientational distribution of CNC nanorods within the liquid crystal structure is presented. This paper illustrates the numerous benefits of using SHG microscopy for visualizing CNC chiral nematic systems directly in the suspension-liquid phase and paves the road for using SHG microscopy to characterize other types of aligned CNC structures, in wet and dry states.

Solvatochromism, electric dipole moments, optical properties and electronic structure of biphenylcarbonitrile liquid crystals

The UV–Vis. absorbance and fluorescence spectra of 4HC (4′-heptyl-4-biphenyl carbonitrile) and 4OB (4′-Octyl-4-biphenylcarbonitrile) liquid crystals were measured in 23 solvents with different polarities. As dependent on changing of solvents, while the change in absorbance spectrum of liquid crystals have less, change in fluorescence spectrum have more. Molecular interactions were quantitavely investigated by using Linear solvation energy relationships. Optical forbidden energy gap has been determined with using Tauc plot. The refractive index has been calculated with semi-empirical methods. The relationships between refractive index and Eg has been commented in n-hexane, acetic acid, water and 1,4-dioxane. The electric dipole moment has been calculated by using the Bilot-Kawski, Lippert-Mataga, Bakshiev, Kawski-Chamma-Viallet and Reichardt methods. Solvatochromic shifts showed to having large dipole moments of 4OB and 4HC LCs. Their molecular orbital energies, electric dipole moments, MEP, SAS, and reactivity properties of 4HC and 4OB LCs has been found by quantum chemical calculations. It was observed that the dipole moment of 4HC was higher than 4OB.

Curvature-directed anchoring and defect structure of colloidal smectic liquid crystals in confinement.

Rod-like objects at high packing fractions can exhibit liquid crystalline ordering. By controlling how the rods align near a boundary, i.e. the anchoring, the defects of a liquid crystal can be selected and tuned. For smectic phases, the rods break rotational and translational symmetry by forming lamellae. Smectic defects thereby include both discontinuities in the rod orientational order (disclinations), as well as in the positional order (dislocations). In this work, we use experiments and simulations to uncover the geometrical conditions necessary for a boundary to set the anchoring of a confined, particle-resolved, smectic liquid crystal. We confine a colloidal smectic within elliptical wells of varying size and shape for a smooth variation of the boundary curvature. We find that the anchoring depends upon the local boundary curvature, with an anchoring transition observed at a critical radius of curvature approximately twice the rod length. Surprisingly, the critical radius of curvature for an anchoring transition holds across a wide range of rod lengths and packing fractions. The anchoring controls the defect structure. By analyzing topological charges and networks composed of maximum density (rod centers) and minimum density (rod ends), we quantify disclinations and dislocations formed with varying confinement geometry. Circular confinements, characterized by planar anchoring, promote disclinations, whereas elliptical confinements, featuring antipodal regions of homeotropic anchoring, promote long-range smectic order and dislocations. Our findings demonstrate how geometrical constraints can control the anchoring and defect structures of liquid crystals-a principle that is applicable from molecular to colloidal length scales.

Twist disclinations mediated transformations in confined nematic liquid crystals

We studied numerically structural transformations in different confined nematic liquid crystals (LC) mediated by chargeless (twist) disclinations. Firstly, we focus on the role of twist disclinations in Moiré-type geometrical setup where LC is confined in a plane-parallel cell. We impose an azimuthal rotation to initially parallel wedge disclinations where the total topological charge of the system equals to zero. Two qualitatively different scenarii are observed depending on the cell thickness. In thin enough cells the disclinations touch in the mid-plane which enables continuous transformation into a final structure consisting of two twist disclinations confined to the limiting substrates. On the other hand, in thinner cells an additional chargeless loop is formed in the mid-plane. In this case, on rotating the initially parallel disclinations periodic structural reentrant behavior is observed. In cylindrical geometry we considered transformations between the initial metastable escaped radial structure with point defects (ERPD) into escaped radial (ER) or planar polar structure with line defects (PPLD). In both cases two nearby ring-like point defects within the ERPD structure collide and temporarily form a chargeless twist disclination loop. The latter in the ERPD-ER transformation shrinks and enables continuous transformation into the final thermodynamically stable structure. On the contrary, in the ERPD-PPLD transformation the twist loop, whose local structure matches PPLD configuration, increases and converts the system continuously into the global PPLD configuration. Detailed understanding of chargeless defect mediated transformations is beneficial for development of future switching devices based on continuous nematic structural transformations between LC structures exhibiting significantly different optical features.

Organic-Inorganic Hybrid Silica Film with a TGBA* Structure.

Twisted grain boundary (TGB) phases exhibit highly frustrated and complex liquid crystal structures, and have attracted enormous interest because of their unique internal structure, textures and properties. However, among the few real concerns related to these interesting structures, applying them to prepare polymer-stabilized colored liquid crystal films has been challenging. Herein, the organic-inorganic hybrid silica (OIHS) films with a TGBA* structure were prepared using two organosilanes and one chiral additive under an acidic condition. The structural color of the films can be adjusted by varying the polycondensation temperature and the concentration of the chiral additive. A structurally colored pattern was prepared by the inject printing, which was suitably applied for decoration and anti-counterfeiting.

MODELS OF FALSE AND CORRECT DETECTION OF INFORMATION LEAKAGE SIGNALS FROM MONITOR SCREENS BY A SPECIALIZED TECHNICAL MEANS OF ENEMY INTELLIGENCE

The calculation expressions for the probability of false detection of a leakage signal, taking into account the discrete representation of time in the models of detection of side radiation signals from static images on the monitor screen on liquid crystal structures by a specialised technical means of enemy intelligence, which implements an asymptotically optimal joint algorithm for detecting side radiation signals and estimating the duration of the image on the monitor screen, are refined. For this purpose, a large independent array of noise was generated in the Mathcad software environment, and the process of false signal detection by a specialised enemy intelligence vehicle was modelled in several Excel workbooks under conditions of a priori uncertainty about the duration of a static image on the monitor screen.

The Correlations between Microstructures and Color Properties of Nanocrystalline Cellulose: A Concise Review.

Cellulose nanocrystals (CNCs) are a green resource which can produce photonic crystal films with structural colors in evaporation-induced self-assembly; CNC photonic crystal films present unique structural colors that cannot be matched by other colored materials. Recently, the mechanisms of CNC photonic crystal films with a unique liquid crystal structure were investigated to obtain homogenous, stable, and even flexible films at a large scale. To clarify the mechanism of colorful CNC photonic crystal films, we briefly summarize the recent advances from the correlations among the preparation methods, microstructures, and color properties. We first discuss the preparation process of CNCs, aiming to realize the green application of resources. Then, the behavior of CNCs in the formation of liquid crystal phases is studied, considering the influence of the CNCs' size and shape, surface properties, and the types and concentrations of solvents. Finally, the film formation process of CNCs and the control of structural colors during the film formation are summarized, as well as the mechanisms of CNC photonic crystal films with full color. In summary, considering the above factors, obtaining reliable commercial CNC photonic crystal films requires a comprehensive consideration of the subsequent preparation processes starting from the preparation of CNCs.

Bifocal lenses with adjustable intensities enabled by bilayer liquid crystal structures.

In this paper, we propose bifocal lenses based on bilayer structures composed of a liquid crystal (LC) cell and LC polymer, and the relative intensity of two foci can be adjusted arbitrarily through applying an external voltage. Two LC layers have different light modulation functions: when circularly polarized light passes through the first layer, part of the outgoing light is converted with PB phase modulation and another part is not converted; followed by the second layer, PB modulation of these two parts would be simultaneously realized but with opposite signs; thus the transmitted left- and right-handed circularly polarized (LCP and RCP) light can be independently controlled. As proof-of-concept examples, longitudinal and transverse bifocal lenses are designed to split an incident LCP light into two convergent beams with orthogonal helicity, and the position of the two foci can be flexibly arranged. Benefitting from the electrically controlled polarization conversion efficiency (PCE) of the LC cell, the relative intensity of the two foci can be adjusted arbitrarily. Experimental results agree well with theoretical calculations. Besides, a broadband polarization and an edge imaging system based on the proposed bifocal LC lenses have also been demonstrated. This paper presents a simple method to design a functional multilayer LC device and the proposed bifocal lenses may have potentials in the optical interconnection, biological imaging, and optical computing.

Study on the influence of oils on the formation of liquid crystal structure of hydrogenated lecithin system

ABSTRACT Hydrogenated lecithin (HLC) is a liquid crystal emulsifier which can be oriented at the oil-water interface to form a long-range ordered and short-range disordered liquid crystal (LC) structure. In this study, the effects of oils commonly used in cosmetics (white oil, squalane, caprylic/capric triglyceride, Jojoba seed oil, shea butter) on the formation of LC structure for HLC system were investigated. The results showed that the numerous LCs was formed when the mass ratio of cetostearyl alcohol/HLC exceeded 8/2 in a single oil system. Among them, the liquid crystals formed by white oil and shea butter were more orderly. Meanwhile, the content of different oils also had a certain impact on the amount of liquid crystal. In this regard, the influence of compound oil system on liquid crystal was further studied by regulating the proportion and type of oils. It was found that the LC area was the largest and the LC structures were relatively regular when squalane/caprylic/capric triglyceride/shea butter was compounded. This study provided certain experimental basis and references for the development of LC emulsion formulations of hydrogenated lecithin system.

Stable hierarchical ionic liquid nanochannels for highly efficient CO2 adsorption, separation and conversion

Constructing stable nanochannels and nanoconfined environments for ionic liquids holds significant application value in gas separation, ion channels, and related fields. The functional polyionic liquid synthesized in this study exhibits a controllable assembly structure and demonstrates liquid crystal properties. Through heating and water treatment, the polyionic liquids crosslink to form multi-hierarchical nanopores, including sub-nanochannels with pore sizes similar to CO2, without the need for a catalyst. The specific surface area and pore size of the polyionic liquid network (PILC) were adjusted by regulating the self-assembly of polyionic liquids in water. The unique PILC, combining ionic liquid nanopores and liquid crystal structure properties, shows high CO2 adsorption performance and excellent CO2/N2 selectivities, surpassing commonly reported ionic liquid porous materials. Furthermore, PILC-2 exhibits good catalytic performance for CO2 cycloaddition, and its catalytic activity and selectivity did not significantly decrease after five cycles. This study successfully introduces hierarchical ionic liquid nanochannels into porous networks without involving any inorganic ordered nanomaterials. This provides a simple and effective approach for the highly selective adsorption and separation of CO2, as well as for the preparation of catalytic materials.

Electro-optical effect of unpolarized light modulation in homeoplanar structures of ferroelectric and ferrielectric liquid crystals.

A clearly expressed effect of unpolarized light electro-optical modulation by homeoplanar structures of a smectic C* ferroelectric liquid crystal (FLC) and a ferrielectric liquid crystal (FerriLC) was discovered and investigated for the first time to our knowledge. This effect of electrically controlled light scattering is insensitive to the applied voltage sign, as for polymer-dispersed nematic liquid crystals (PDLCs), but the electro-optical modulation frequency reaches the kilohertz range. Occurrence conditions and essential features of the effect, as well as its physical origin, are discussed.

Construction of Nano-Janus emulsion by phase inversion composition

Nano-Janus emulsion possesses excellent solubilization capabilities of both aqueous and organic materials, various liquid–liquid interfaces, and precisely controllable morphology. Successful construction of nano Janus droplets at mild conditions of room temperature and low-energy input will expand the industrial application. Two immiscible liquids of silicone oil (SO) and oleic acid (OA) are used as internal phases, and water is added dropwise at mild temperature. The topology of the nano-sized complex droplets is characterized by cryo-TEM, SAXS, and FF-TEM. Micro structure of lamellar liquid crystal (Lα), which is the critical transition phase, is investigated to reveal the formation mechanism. Topology adjustment including size range, volume ratio, and interface curvature is investigated. Complex nano droplets with snowman shape are successfully constructed in batch-scale at mild temperature of 30 °C and water-dripping rate of 1.0 mL/h. Formation of a four-component Lα phase is the critical point to the successful construction of the nano-Janus emulsion, which also creates additional freedom for structural regulation. The size of the complex droplets is freely alternated in the range of 50–500 nm and the morphology of one lobe is controlled from “crescent” to “half-moon”, and “moon with a hole”.

Liquid crystal-based reconfigurable antenna for 5G millimeter-wave

This paper proposed a frequency reconfigurable antenna that utilizes a multilayer structure of liquid crystal (LC) material. This antenna design incorporates a three-layer stacked structure to create an LC-injected cavity. The inverted microstrip line structure is designed to be in contact with the LC, serving as both a radiating element and a bias electrode. A parasitic patch is placed at the top of the antenna to enhance bandwidth. To prevent interference with DC and RF sources, a bias tee is integrated into the microstrip line input. Experimental results demonstrate that the proposed antenna exhibits excellent impedance matching and stable radiation patterns within the operational frequency range. By comparing the simulated performance of the existing LC antenna with our proposed design, the bandwidth is tripled at a center frequency of 30.3 GHz. In addition, the effective area of the proposed reconfigurable antenna (154 mm2) is 24.6% of the area of the previous reconfigurable antenna (625 mm2).